The present invention relates generally to the field of communication with a secure data link using a transmitter with a phased antenna array.
There are many forms of secure data links for radio transmission using various types of coding. Although not directed to security, a book by Henning F. Harmuth, Transmission of Information by Orthogonal Functions, 2nd ed. New York/Heidelberg/Berlin:Springer-Verlag, 1972, is of interest.
Phased array antenna systems are also well known, as shown for example in the text by Skolnik, "Introduction to Radar Systems" 2nd ed. Chapter 8; or in the "Radar Handbook" edited by Skolnik, Chapter 11. U.S. Pat. No. 3,723,955 to Lyons et al discloses a sonar beam generating apparatus in which the generated beam is shifted between 0.degree. and 180.degree. by an array of transducer elements. U.S. Pat. No. 3,697,994 to O'Daniel discloses a digital computer system for steering the pencil beam of a 3-D cylindrical array radar antenna. The beam is steered in both elevation and azimuth by selectively energizing binary phase shifters associated with each radiating element of the array. U.S. Pat. Nos. 4,034,374; 3,646,558; 3,999,182; 3,747,098; 3,478,359; and 3,864,689 disclose a variety of antenna systems with phase shifters which are of general interest.